Coat a small nonstick skillet with cooking spray. Warm the skillet over medium heat. Pour the egg product into the skillet. Lift and tilt to form a thin egg sheet.
Cook the egg product, without stirring, for about 2 minutes or until just set. Remove from heat. Remove egg sheet from skillet. Cool completely. Cut egg sheet into 1/4-inch squares. Set aside.
Meanwhile, in a covered saucepan, cook the potatoes in boiling water 15 to 20 minutes or until just tender. Drain.
In a large mixing bowl, combine chopped egg, potatoes, green onions, and celery. In another bowl, stir together sour cream, mayonnaise, pickle relish, parsley, mustard, garlic (if you like), pepper, and salt. Toss with potato mixture. Cover and chill for at least 6 hours or up to 24 hours. Makes 4 side-dish servings.